NavList:

Brad wrote:

I fear that the high frequency accelerations associated with a hand held device such as proposed will preclude an accurate vertical. One only has to download one of the free apps *(such as Accelogger on the Android system) to observe the noise present. This noise is the same issue that precludes inertial navigation using your cell phone, many have tried, all have failed. Simply search for "inertial navigation" for your cell phone. I know I want that application.
Sure, the phone understands which way is generally down, so as to orient the screen, but that is far from understanding fine resolution vertical.
So holding the device will most likely not work with chips present in modern smart or cell phones.
___________

This brings up bandwidth considerations. The accelerometers in cell phones and game controllers are intended for a broad range of applications, some of which require a quick response to hand motions. This implies a bandwidth of probably more than 10 Hz. For a star sighter application, the bandwidth needs are much, much less. It would be highly advantageous to low pass filter the accelerometer outputs with a cutoff of 1 Hz or less. Perhaps as low as .1 Hz might work well in reducing the errors of external vibration. Additionally, it would significantly reduce an inherent noise source in all MEMS accelerometers that is proportional to the square root of the bandwidth. As an example, the ADXL203 has a noise limitation of about 1 mg when operated with a 60Hz bandwidth, an order of magnitude too great for celestial navigation. But add on a .1Hz low pass filter and this error source drops down to an acceptable level.

My suspicion is that a hand held device will still be unpractical, but I do hold out hope for a well-damped tripod.

Don Seltzer

----------------------------------------------------------------
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com
----------------------------------------------------------------